Transcript Air Masses and Fronts

Air Masses and Fronts
Weather
How Do Air Masses Affect
Weather?
• Weather maps show that cities
across a large region share the
same weather and they also
show how the weather in
different areas differs.
• A large region of the atmosphere
where the air has similar
properties throughout is called
an air mass.
• An air mass gets its properties
from the region where it forms.
Air Masses
• Air masses are named for the region they
come from.
• Example, Air over the Gulf of Mexico is
above very warm water. The water warms
the air, and evaporation from the Gulf adds
water vapor. The air becomes warm and
moist.
Air Masses
•
•
•
•
Maritime polar (mP) – cool, moist air
Continental polar (cP) – cold, dry air
Maritime tropical (mT) – warm, moist air
Continental tropical (cT) – hot, dry air
• Once an air mass is formed, it is moved by
global winds. In the United States, global
winds tend to move air masses from west
to east.
• Air masses with different conditions can
“meet.” That is, one runs into another.
• What happens when air masses with
different temperatures meet? They don’t
mix together. Instead, a narrow boundary
forms between them. This boundary is
called a front.
• The boundary marks the leading edge, or
front, of an air mass that is moving into an
area where another air mass is moving
out. Weather changes rapidly at fronts.
That’s because you pass from one kind of
air mass into another. Fronts often cause
rainy, unsettled weather.
A Weather Front
How Do Fronts Affect Weather?
Cold Front:
In a cold front, cold air moves in under
warm air mass. Cold fronts bring brief,
heavy storms. There may be
thunderstorms and strong winds. After the
storm the skies are usually clearer, and
the weather is usually cooler and drier.
Warm Front:
In a warm front, warm air moves in over a
cold air mass. Warm fronts often bring
light, steady rain or snow. The precipitation
may last for days. Winds are usually light.
Warm fronts may also bring fog—stratus
clouds that form near the ground.
Afterward the weather is usually warmer
and more humid.